Month: December 2014

how can we check congestion on link and what all parameters and commands to check , if there is congestion on link . what all possible reason for congestion . what all possible steps for troubleshooting with commands

Sumit SharmaFahad Ahmed .. WAN optimizer is a separate dedicate device. Its purpose is to utilize its mechanism, compression is part of mechanism in such a way that Bandwidth requirement is reduced. Most common is Steelhead Riverbed.

Sumit SharmaIn Steelhead Riverbed, There is one feature, We have the option of checking Top Talkers List, which tells us which ip or user or device is utilizing maximum bandwidth with exact amount of data.

Sumit SharmaHOW TO CHECK CONGESTION ?———————————–OPTION 1: Check Live traffic, using command show interface summary———————————–OPTION 2: NFA is Netw Flow Analyezer.If NFA is configured, NFA also captures the traffic over different interfaces with more details———————————–OPTION 3: If Riverbed is configured, we have feature called Top Talkers List to check exact amount of data for every ip———————————–If the utilization is normal at a particular time, we need to observe the traffic trend at the peak time or office business hours

Sumit SharmaIf you know that there is congestion in the network, it means you already got the output that yes bandwidth utilization is high——————————Normally, problem comes in like LATENCY in the network, for that one of the reason can be the congestion.——————————

Sumit SharmaSOLUTION————–OPTION 1: Increase the Bandiwdth————–OPTION 2: Deploy WAN optimizer device like Steelhead Riverbed————–OPTION 3: Most of the time what happens is Two different servers are communicating with each other for backup. This traffic is utilization is maximum proportion of Bandwidth.Solution is to dedicate separate link for critical Datacenter servers communication or traffic————-OPTION 4: Simply find the culprit user & try to decrease the utilization ————–

Binoj SasidharanLayer 2 broadcasts are sent to the broadcast mac address ffff:ffff:ffff if ethernet and so can be received by any device in the same broadcast domain . Layer 3 broadcasts are sent to the broadcast network address, which for an ip network of 10.1.1.0/24 would be 10.1.1.255. If the IP network was over ethernet, a layer 3 broadcast would also result in a layer 2 broadcast

Abhi SinghBroadcast frames usually have a hosts MAC/IP address in the SA field.An example of a layer 2 broadcast is an ARP Request.in an ARP request Host A [IP=10.1.1.5 MAC=AA:B2.CD] knows the destination IP I want [10.1.1.11], but do not know the destination MAC address, so it is a unicast L3/broadcast L2.Frame [dMAC=ff:ff:ff][sMAC=AA:B2:CD][dIP=10.1.1.11][sIP=10.1.1.5][PDU]An example of a layer 3 broadcast is DHCP DISCOVER. My host knows its own MAC but doesn’t know my IP, I don’t know the destination IP or MAC so is broadcast L3 and broadcast L2Frame [dMAC=ff:ff:ff][sMAC=AA:B2:CD][dIP=255.255.255.255][sIP=0.0.0.0][PDU]

Sumit SharmaLAYER 2 BROADCAST==> broadcast L2 frame has the dst MAC set to ff-ff-ff-ff-ff-ff.==> Means broadcast will be done in a particular subnet only.So, Broadcast will stay inside the boundary of a single network or single subnet, where broadcast originated

Sumit SharmaLAYER 3 BROADCAST==> broadcast L2 frame has the dst IP set to 255.255.255.255==> Means Broadcast will be done in all the subnets present in the network.So, Broadcast will cross the boundary of a single network or single subnet., where broadcast originated

Sumit SharmaLAYMAN EXAMPLE ==> During Route Summarization, loop might occur.Example: If traffic comes for a network which lies in the summarized range, but actually network do not exist.==> To avoid this, by defaut, Discard route is installed.

Sumit SharmaIn above example,==> 172.16.0.0/24 is the summarized address==> If traffic comes for 172.16.0.128/25, exact route is present==> If traffic comes for 172.16.0.126/25, which is not present. So, Discard route pointing to Null0 will be prefered==> By this, Traffic will go back to the sender, that is ABR

Anubhav Srivastavatrue bro, I understand this Null0 interface route in the table. I got this issue when this discard route was learned via ospf, showing no interface for next hop. Yes, device was juniper router

PAGE – MONITOR – SUMMARY

==> In Access Point Summary, All APs = 5, which is showing the total number of associated AP’s. Click on details for further information.

==> In Access Point Summary, 802.11 a/n & 802.11 b/g/n are showing different bands. In front of them, total number of AP’s are given supporting these bands

==> In Client summary, shows the user’s connected to WLC. Click on details for further information.

PAGE – MONITOR – SUMMARY

COMMENTS

==> Details shown are list of all AP’s

==> Authentication used between AP & WLC is Internal Authorization. Internal Authorization means authentication using certificates, not using any external server. Here, certificate type is MIC. Other options are SSC, LSC.

==> Uptime for all the Ap’s are shown

==> AP mode is local. Other possible mode can be Flex connect mode.

PAGE – MONITOR – STATISTICS – AP JOIN

PAGE – MONITOR – STATISTICS – PORTS

PAGE – MONITOR – STATISTICS – RADIUS

PAGE – MONITOR – CDP – INTERFACE NEIGHBORS

COMMENTS

==> Here, Gi0/0/1 & Gi0/0/2 are the ports on WLC.

==> In Neighbor name, connected devices host name is shown. Neighbor ip is the ip of connected devices to WLC.

==> Gi0/2 & Gi0/3 are the ports of connected devices

PAGE – MONITOR – CDP – AP NEIGHBORS – CLICK DETAILS

COMMENTS

==> AP Name shows associated AP’s

==> Neighbor Name shows the name of connected devices, which should be a switch. Neighbor address is the ip address of the connected switch. Neighbor port is the connected port on switch.

will appreciate your helps on it.

Thanks!!

Sarvesh DubeyHi Manjunath S Chickmath thanks for the reply, can you please share the way to check QOS on juniper router……..by the way the links belong to service provider itself for DCN , so As per my understanding QOS wouldn’t be an issue here

Sampath KumarDude remove the ISP cable from your switch put it directly to ur PC. configure static ip with the public provided by the ISP, now check the Bandwidth speed if u r getting 4MBPS only give a hard kick to isp provider. If you r getting the full bandwidth in your PC, then case1: any huge downloads may be going on, try to find in that way. case2: QOS policy is done on router or firewall to check that go through the running config of entire router(by using “|” (pipe symbl) may reduce ur burden). if qos is enabled remove it.

Manish Yadavfor eg the router has capability of 160Mb . On router one 80 Mb link is terminated (i.e;occupied) and also other parameters consume bandwidth like hello,encryption,etc. remained with 40% of 160MB.

Sumit SharmaLittle Probing I will do. ( 1) first confirm if at PE end, capping is actually done for 144. ( 2 ) If things are OK at ISP, we need to verify from our end if we are getting the committed speed, for testing I recommend do not check live traffic or some download which will obviously do not show the actual bandwidth. Go for some third party software which pushes traffic to the maximum limit on the link, which is equal to bandwidth of link.

Manjunath S ChickmathWhen BGP tries to install the “bestpath ” prefix into Routing InformationBase (RIB) (for example, the IP Routing table), RIB might reject the BGP routedue to any of these reasons:· Route with better administrativedistance already present in IGP. For example, if a static route already existsin IP Routing table.· Memory failure.· The number of routes in VPNrouting/forwarding (VRF) exceeds the route-limit configured under the VRFinstance.In such cases, the prefixes that arerejected for these reasons are identified by r RIB Failure in theshow ipbgp commandoutput and are not advertised to the peers.

Chakkaravarthi VinayagamIn layered architecture we can’t route the packets with the help of #MAC_address if we do so our entire internet domain act as a single cluster. If we use #IP_address we can create multiple cluster like what we have in today internet domain. We can able to identify problems and avoid unnecessary routing into our private network.

Rytesh Vishwakarmaip is used to locate the networkMac is used to locate the host on that network.While communicating with remote hosts we dont use the mac of the destination host instead we use the mac of our default gateway….Our ip takes us to that network afterwards we use arp to find the mac of the destination host.

Rytesh Vishwakarmaip is used to locate the network Mac is used to locate the host on that network. While communicating with remote hosts we dont use the mac of the destination host instead we use the mac of our default gateway…. Our ip takes us to that network afterwards we use arp to find the mac of the destination host.

Cisco SahilAjay Kumar .. Yes you are right, using Layer 2 trace route & Layer 3 trace route, we can understand complete network. This is the mechanism to understand. But we need to go into background to understand the designing basics of MAC address & IP.

Mohammed Yunusmac address is identification , and Ip is an address , for ex : post letter Name is identification (mac) and Address is IP , without name or address we cont send the letter , that’s like mac and Ip

Mohammed Yunusmac address is identification , and Ip is an address , for ex : post letter Name is identification (mac) and Address is IP , without name or address we cont send the letter , that’s like mac and Ip

Sumit SharmaOne very good logic given by candidate: MAC address is used for identification, true, But MAC addresses cannot be summarized, Individually they could have made the routing table very large, which is impossible to be handled by the network devices. Whereas, IP’s can be summarized, this is what we are doing in our network, that’s why network devices are able to handle routing tables.

Manish SharmaHi….the reason could be for mac- address there is no hierarchy…..so it would be difficult to separate one network from another….but for IP addressing we can logically divide this and thus it is used …

Noor Mohamad Kanjwalmac address r like finger print… its uniq 4 every human but we use names to identfy them ..same way we use ip address to identfy ny device..its logical address easy to use n remember than mac address

Mohamed Salmanthis was my ques when i just started ccna and i ended up makin my own ans just as Sumit Sharma mentioned…but my way of thinkin ws ip address is kinda standard and everyone uses the same standard whc ends up doin SUMMERIZATION ..but when it comes in terms of MAC the 1st part is vender specific..if som new vender comes up tomm then he will make up his own range of MAC which would mess up things if we are communicating in wan in terms of MAC.. i hope i was able to keep my thought

Sumit SharmaOne thing: SCALABILITY: IP’s have standard format, MAC address don’t have ( Varies from vendor to vendor ). So, there cannot be summarization. Without summarization, Its not feasible at all to handle routing table in live environment. This is a strong reason, we are using ip’s.